User interfaces for consumer electronics devices commonly employ physical buttons to allow a user to control device functions. For example, a cell phone may have dozens of buttons distributed in various locations around the device to allow a user to answer calls, navigate through operating system menus, etc. Some devices may also permit a user to control a device by tilting or shaking it. In such devices, motion induced by the user may be sensed using accelerometer integrated circuits (ICs) and particular motions may then be correlated with device functions. However, motions such as tilting, shaking, etc. may interfere with the user's enjoyment of the device by, for example, interrupting viewing of a device's display, contributing to a user's repetitive motion injuries, etc.
Some products may also allow a user to interact with a device by tapping it. For example, an accelerometer IC may be employed to distinguish the act of a user tapping a device's case from other events such as the user tapping the device's physical keys.